MFC r315900,r315973,r315974:

r315900:
Cleanup structures related to VFP and/or mcontext_t. - in mcontext_t,
rename newer used 'union __vfp' to equaly sized 'mc_spare'.
Space allocated by 'union __vfp' is too small and cannot hold full VFP
context.
- move structures defined in fp.h to more appropriate headers. - remove
all unused VFP structures.
r315973:
Save VFP state on fork(). Update the copy of VFP state in PCB before it is
cloned for new process.
r315974:
Preserve VFP state across signal delivery.

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

SMP support for ARMv6/v7 HW watchpoints

Use per-CPU structure to store HW watchpoints registers state
for each CPU present in the system. Those registers will be restored
upon wake up from the STOP state if requested by the debug_monitor
code. The method is similar to the one introduced to AMD64.

We store all possible 16 registers for HW watchpoints
(maximum allowed by the architecture).
HW breakpoints are not maintained since they are used for single
stepping only.

Pointed out by: kib
Reviewed by: wma
No strong objections from: kib
Submitted by: Zbigniew Bodek <zbb@semihalf.com>
Obtained from: Semihalf
Sponsored by: Juniper Networks Inc.
Differential Revision: https://reviews.freebsd.org/D4338

Protect the function declarations with #ifdef _KERNEL.

Import FreeBSD/arm kernel bits.
It only supports sa1110 (on simics) right now, but xscale support should come
soon.
Some of the initial work has been provided by :
Stephane Potvin <sepotvin at videotron.ca>
Most of this comes from NetBSD.